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    <script>
        // 1、求1 + 2！ + 3！ + 4！....+20!的值
        //     - 2！ = 2 * 1   
        //     - 3！ = 3 * 2 * 1
        var k = 1
        var h = 0
        for(var i = 1; i <= 20 ; i++){
            k *= i
            h += k
        }
        console.log(h)
    </script>
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